In U.S. Pat. No. 3,938,640, there is disclosed a selector mechanism adjustable to accommodate a lock unit for operation by a group of coins defined by a desired number of coins of a given denomination. This lock unit has the advantage of permitting accurate gauging of deposited coins with a minimum of structural parts subjected to wear and/or failure. However, a drawback of this prior construction is that the lock unit may be rendered inoperative, when an improper or mixed denomination group of coins are inserted into the lock unit; this requiring the attention of a custodian to remove the lock unit from its locker cabinet. Another drawback of this prior construction is that it cannot be readily mounted as a replacement for previously installed lock units of the type disclosed for instance in U.S. Pat. Nos. 3,228,506 or 3,599,770, when it is desired to increase the charge for use of such lockers.
In U.S. Pat. No. 3,613,855, there is disclosed a two-coin operated lock having the capability of discharging coins of a diameter smaller than the diameter of a given coin denomination regardless of whether such coins were deposited before or after the first coin of such given denomination. Thus, for a two-coin grouping, the construction of the lock unit disclosed by this patent avoids the above mentioned drawback of the lock unit construction discosed in U.S. Pat. No. 3,938,640. However, selector mechanism of U.S. Pat. No. 3,613,855 is difficult to adust to handle coins of a denomination differing from that for which the lock unit was originally designed; there is a possibility of jamming the coin chute and/or selector mechanism of the lock unit, if coins are deposited after the two proper or given denomination coins; and the selector mechanism of this patent is not readily adapted for use with the basic lock unit construction disclosed for instance in U.S. Pat. Nos. 3,228,506 and 3,599,770, such basic lock unit construction possessing certain advantages when compared to that of U.S Pat. No. 3,613,855.